400 Bad Request when calling V3 API to get Campaign

One of my client getting this error when calling the V3 api to get campaign detail. Can you please let me know 'why the campaign type is not supported'?

GET callout:CTCT/v3/emails/6da4e95f-5c3a-4005-9c47-2f6434f83255

Code: 400

[
{
"error_key": "email.emailcampaign.retrieve.badrequest",
"error_message": "Unable to retrieve Email Campaign information because this campaign type is not supported"
}]